Coated cutting tool and method for producing the same

ABSTRACT

Provided are a coated cutting tool having excellent wear resistance and excellent resistance to chipping as well as excellent fracture resistance such that the coated cutting tool is unlikely to cause backward movement of the tool edge position due to wear or chipping, and a method for producing the same. 
     A coated cutting tool comprising a base material having a surface coated with a coating film, wherein the coating film comprises at least one layer comprised of a TiCN columnar crystal film, wherein the TiCN columnar crystal film has an average grain size of 0.05 to 0.5 μm, as measured in the direction parallel to the surface of the base material, and exhibits an X-ray diffraction pattern having a peak at a diffraction angle 2θ in the range of from 121.5 to 122.6° wherein the peak is ascribed to the ( 422 ) crystal facet of the TiCN columnar crystal as measured using CuKα radiation.

FIELD OF THE INVENTION

The present invention relates to a coated cutting tool comprising a basematerial having a surface coated with a coating film. More particularly,the present invention is concerned with a coated cutting tool whichcomprises a base material having a surface coated with a TiCN columnarcrystal film having a specific structure, and which is advantageouslyused in cutting for ductile cast iron, carbon steel, and others.

BACKGROUND ART

A coated cutting tool, which comprises a base material comprised of ahard material having a surface coated with a TiCN columnar crystal filmdeposited by a chemical vapor deposition (CVD) method at amedium-temperature such as a temperature in the range of from 700 to900° C. using raw material gas comprising CH₃CN wherein the TiCNcolumnar crystal film is coated with an aluminum oxide film, is widelyused in cutting.

As a prior art coated cutting tool, there is a surface-coated cuttingtool made of tungsten carbide-based cemented carbide, which is coatedwith a first layer comprised of titanium nitride, a second layercomprised of titanium carbo-nitride, a third layer comprised of titaniumcarbo-oxide, and a fourth layer comprised of aluminum oxide (see, forexample, patent document 1). However, since the surface-coated cuttingtool made of tungsten carbide-based cemented carbide is coated with atitanium carbo-nitride film deposited by a medium-temperature CVD methodusing raw material gas comprising CH₃CN, the atomic ratio of carbon tothe sum of carbon and nitrogen contained in the titanium carbo-nitridefilm {C/(C+N)} is as small as 0.5 to 0.6. Therefore, there is a problemin that the titanium carbo-nitride coating film has a low hardness andhence does not exhibit a satisfactory wear resistance.

As another prior art coated cutting tool, there is a coated cutting toolcoated with a TiCN film using raw material gas comprising CH₃CN and CH₄(see, for example, patent document 2). However, when the reaction fordeposition is conducted at a temperature of 900° C. or lower, only CH₃CNis reacted and almost no CH₄ undergoes the chemical reaction. Therefore,the resultant TiCN film does not have a C/(C+N) ratio of more than 0.6,and thus the TiCN film has a low hardness and does not exhibit asatisfactory wear resistance. On the other hand, when the reaction isconducted at a temperature of higher than 900° C., the resultant TiCNcoating film is comprised of coarse crystal grains, and hence is loweredin toughness, causing a problem in that the fracture resistance is poor.

[Patent document 1] Japanese Unexamined Patent Publication No. Hei07-328808

[Patent document 2] Japanese Unexamined Patent Publication No. Hei06-158324

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

In recent years, in the field of machining, there are increasing demandsfor machined products having high quality, particularly having animproved accuracy of machining dimension. Further, the materials to becut are increased in hardness or they become more difficult to cut yearby year, and, when such materials are cut by means of a conventionalcutting tool, backward movement of the tool edge position is likely tooccur due to wear or chipping of the relief surface portion, leading toa disadvantage in that the machining dimension of the materials to becut falls outside of the prescribed range in a short machining time. Inthe machining sites, for keeping the accuracy of the machining dimensionof the materials to be cut within the prescribed range, the tool edgeposition is frequently corrected, which lowers the machining efficiency.Therefore, a cutting tool more unlikely to cause backward movement ofthe tool edge position has been desired by the machining sites.Accordingly, an object of the present invention is to provide a coatedcutting tool having excellent wear resistance and excellent resistanceto chipping as well as excellent fracture resistance such that thecoated cutting tool is unlikely to cause backward movement of the tooledge position due to wear or chipping, and a method for producing thesame.

Means to Solve the Problems

The present inventors have conducted extensive and intensive studieswith a view toward developing a coated cutting tool unlikely to causebackward movement of the tool edge position due to wear or chipping ofthe tool edge. As a result, it has been found that, when a TiCN columnarcrystal film is deposited on the surface of a base material by amedium-temperature CVD method at 700 to 900° C. using raw material gascomprising an organic cyanogen compound, such as CH₃CN, a chainhydrocarbon having carbon atoms of from 2 to 20 thus excluding CH₄, suchas C₂H₄, C₂H₆, C₃H₆, or C₃H₈, titanium tetrachloride, and hydrogen, theresultant TiCN columnar crystal film is increased in hardness withoutlowering the strength, as compared to a conventional TiCN film depositedwithout using the chain hydrocarbon excluding CH₄. The coated cuttingtool obtained by the present invention has excellent wear resistance andexcellent resistance to chipping as well as excellent fractureresistance. Therefore, backward movement of the tool edge position dueto wear or chipping is suppressed, making it possible to keep anaccuracy of the machining dimension and to reduce the operationscorrecting the tool edge position due to the change of dimension.

The coated cutting tool of the present invention comprises a basematerial having a surface coated with a coating film, wherein thecoating film comprises at least one layer comprised of a TiCN columnarcrystal film. Specifically, in the present invention, a TiCN columnarcrystal film is formed directly on a base material or formed through aninnermost film formed on the base material. The TiCN columnar crystalfilm has an average grain size of 0.05 to 0.5 μm, as measured in thedirection parallel to the surface of the base material, and exhibits anX-ray diffraction pattern having a peak at a diffraction angle 2θ in therange of from 121.5 to 122.6° wherein the peak is ascribed to the (422)crystal facet of the TiCN columnar crystal as measured using CuKαradiation.

Specific examples of the coated cutting tools of the present inventioninclude cutting chip, end mill, drill, and reamer. The base materialused in the coated cutting tool of the present invention is a materialwhich has conventionally been used as a base material in the coatedcutting tool, and specific examples include cemented carbide, cermet,ceramic, and sintered materials of cubic boron nitride. Cemented carbideis more preferred as the base material in the coated cutting tool of thepresent invention because of the wear resistance and fractureresistance.

The coating film comprising a TiCN columnar crystal film in the presentinvention is comprised of at least one member selected from a carbide, anitride, and an oxide of an element belonging to Group 4a (Ti, Zr, Hf),5a (V, Nb, Ta), or 6a (Cr, Mo, W) of the Periodic Table or Al and amutual solid solution thereof. Specific examples include TiC, TiN, TiCN,TiCO, TiCNO, TiCNO, TiAlCNO, and Al₂O₃. It is preferred that the wholecoating film has an average thickness of 7 to 25 μm. When the wholecoating film has an average thickness of less than 7 μm, the wearresistance becomes poor. On the other hand, when the whole coating filmhas an average thickness of more than 25 μm, the fracture resistancebecomes poor.

The atomic ratio of carbon to the sum of carbon and nitrogen containedin the TiCN columnar crystal film in the present invention {C/(C+N)} ishigher than that of a conventional TiCN film, and the lattice constantof the TiCN columnar crystal film in the present invention is largerthan that of a conventional TiCN film. For this reason, the X-raydiffraction angle 2θ of the peak of the TiCN columnar crystal film inthe present invention shifts to the low angle side, as compared to theX-ray diffraction angle 2θ of the peak of the conventional TiCN film.When the TiCN columnar crystal film in the present invention issubjected to X-ray diffraction using CuKα radiation, the TiCN columnarcrystal film exhibits an X-ray diffraction pattern having a peak at adiffraction angle 2θ in the range of from 121.5 to 122.6° wherein thepeak is ascribed to the (422) crystal facet of the TiCN columnarcrystal. When the diffraction angle 2θ of the peak ascribed to the (422)crystal facet of the film is less than 121.5°, the TiCN film has a highhardness such that the strength of the film is lowered. On the otherhand, when the diffraction angle 2θ is more than 122.6°, the TiCN filmhas a low hardness such that the wear resistance of the film is lowered.The TiCN columnar crystal film has an average grain size of 0.05 to 0.5μm, as measured in the direction parallel to the surface of the basematerial. When the average grain size is less than 0.05 μm, the TiCNcolumnar crystals are extremely fine and hence likely to suffer abreakage. On the other hand, when the average grain size is more than0.5 μm, the TiCN columnar crystal film is lowered in fractureresistance. The average grain size of the TiCN columnar crystal film inthe direction parallel to the surface of the base material can bemeasured by observing the cross-section of the coating film under ascanning electron microscope or a transmission electron microscope.Specifically, the grain size of the TiCN columnar crystal film can beeasily measured by a method in which a cemented carbide base materialhaving a surface coated with a coating film is subjected to heatingtreatment in a vacuum or a hydrogen gas atmosphere at a temperature of1,100 to 1,200° C. for 1 to 90 minutes to diffuse the metallic bondingphase of the cemented carbide base material through the grain boundaryin the TiCN columnar crystal coating film, and then the mirror polishedcross-section of the coating film is observed under a SEM.

In the present invention, it is preferred that a value of the half widthof the peak ascribed to the (422) crystal facet of the TiCN columnarcrystal film is in the range of from 0.40 to 0.60° since the TiCNcolumnar crystal film is improved in fracture resistance. When the valueof the half width of the peak ascribed to the (422) crystal facet of thefilm is 0.40° or more, the average grain size thereof is fine and thefracture resistance thereof is improved. When the value of the halfwidth of the peak ascribed to the (422) crystal facet of the film ismore than 0.60°, the average grain size thereof is too fine and hencethe TiCN columnar crystals are likely to suffer a breakage. Therefore,the value of the half width of the peak ascribed to the (422) crystalfacet of the TiCN columnar crystal film is preferably in the range offrom 0.40 to 0.60°. A value of the half width of the peak ascribed tothe (422) crystal facet of the film can be measured under the followingconditions for measurement.

Characteristic X-ray: CuKα radiation;

Monochromator: Ni;

Divergence slit: ½°;

Scatter slit: ⅔°;

Receiving slit: 0.15 mm;

Sampling interval: 0.01°

In the present invention, it is preferred that the TiCN columnar crystalfilm exhibits an X-ray diffraction pattern having the highest intensityat the peak ascribed to the (422) crystal facet since the toughness ofthe TiCN columnar crystal film is enhanced, improving the resistance tochipping. In the present invention, it is preferred that the TiCNcolumnar crystal film has a C/(C+N) ratio of 0.70 to 0.90. When theC/(C+N) ratio is 0.70 or more, the wear resistance is improved, and,when the ratio is more than 0.90, the fracture resistance tends to belowered.

The TiCN columnar crystal film in the present invention can be depositedusing raw material gas comprising a chain hydrocarbon having carbonatoms of from 2 to 20 thus excluding CH₄, an organic cyanogen compound,titanium tetrachloride, and hydrogen at a deposition temperature of 700to 900° C. Specifically, there can be mentioned conditions fordeposition such that the deposition temperature is 700 to 900° C., thepressure is 5 to 10 kPa, and the raw material gas comprises 1.0 to 4.0mol % of a chain hydrocarbon having carbon atoms of from 2 to 20, 0.1 to0.5 mol % of CH₃CN, 1.0 to 4.0 mol % of TiCl₄, and the balance of H₂.The organic cyanogen compound is both a carbon source and a nitrogensource for the TiCN columnar crystal film and the chain hydrocarbonhaving carbon atoms of from 2 to 20 is a carbon source for the TiCNcolumnar crystal film. Specific examples of the chain hydrocarbonshaving carbon atoms of from 2 to 20 include saturated hydrocarbonshaving a chain structure, such as C₂H₆ and C₃H₈, and unsaturatedhydrocarbons having a chain structure, such as C₂H₄ and C₃H₆. The reasonthat CH₄ with carbon atom of 1 is excluded from the chain hydrocarbonresides in that CH₄ has a high decomposition temperature such that itcannot be a carbon source in the medium-temperature CVD method at adeposition temperature of 700 to 900° C. When the number of carbon atomsfor the chain hydrocarbon is in the range from 2 to 20, the chainhydrocarbon can be introduced into a reaction chamber in a gaseouscondition with other raw material gas in a conventional CVD method. Thisis because that a boiling temperature of the chain hydrocarbon havingcarbon atoms of from 2 to 20 is not so high. Carbon atoms of the chainhydrocarbon are preferably from 2 to 6 and more preferably from 2 to 3.Specific examples of the organic cyanogen compounds include CH₃CN(acetonitrile), CH₃CH₂CN (propanitrile), and C₆H₅CN (benzonitrile).

In the present invention, it is preferred that the TiCN columnar crystalfilm is formed by a medium-temperature CVD method at a depositiontemperature of 700 to 900° C. The reason for this is as follows. Whenthe deposition temperature is lower than 700° C., a chemical reactionfor forming TiCN is unlikely to proceed, so that the deposition time isprolonged, lowering the productivity of the film. On the other hand,when the deposition temperature is higher than 900° C., the averagegrain size of the TiCN columnar crystal film in the direction parallelto the base material is coarsened, deteriorating the fracture resistanceof the film.

The coated cutting tool of the present invention can be produced by amethod for producing a coated cutting tool, comprising the steps of:elevating the temperature of a base material to a depositiontemperature; depositing on the base material a TiCN columnar crystalfilm by a CVD method at a temperature in the range of from 700 to 900°C. using raw material gas comprising a chain hydrocarbon having carbonatoms of from 2 to 20, an organic cyanogen compound, titaniumtetrachloride, and hydrogen; and cooling the base material coated with acoating film.

In the present invention, it is preferred that the TiCN columnar crystalfilm has an average thickness of 5 to 20 μm. When the average thicknessof the film is less than 5 μm, the wear resistance at the relief surfaceis poor. On the other hand, when the average thickness is more than 20μm, the tool edge is likely to suffer fracture. It is more preferredthat the TiCN columnar crystal film has an average thickness of 7 to 15μm.

Since aluminum oxide has excellent oxidation resistance, it is preferredto have an outer film comprising at least one layer of aluminum oxidefilm. The TiCN columnar crystal film of the present invention ispreferably formed directly on the base material or formed on theinnermost TiN film formed on the base material. The aluminum oxide filmin the present invention preferably has an average thickness of 1.5 to10 μm, further preferably 3 to 8 μm. When the average thickness of thealuminum oxide film is less than 1.5 μm, the cutting tool has anunsatisfactory crater wear resistance at the cutting face. On the otherhand, when the average thickness is more than 10 μm, the tool edge islikely to suffer fracture. It is preferred that the aluminum oxide filmhas an α-type crystal structure since the α-aluminum oxide is morestable at high temperatures than aluminum oxide of the other crystalstructure. The α-aluminum oxide film is unlikely to cause fracture orchipping when the tool edge is at a high temperature in the high-speedcutting particularly for carbon steel or alloy steel.

Effect of the Invention

The coated cutting tool of the present invention exhibits excellent wearresistance and excellent resistance to chipping as well as excellentfracture resistance. When using the coated cutting tool of the presentinvention, backward movement of the edge position due to wear orchipping is advantageously suppressed, thus making it possible to keepan accuracy of the machining dimension of the material to be cut and toreduce the operations correcting the tool edge position.

EXAMPLE 1

As a base material, a cutting chip made of cemented carbide, having aCNMG120412 form specified in JIS, and having a composition: 91.5 wt %WC-0.5 wt % TiC-1.8 wt % TaC-0.2 wt % NbC-6.0 wt % Co, was prepared. Thecutting edge portion of the base material was subjected to round honingby means of a SiC brush, and then the surface of the base material waswashed. Then, the resultant base material was placed in a CVD chamberwith an external heating system, and a coating film was deposited on thesurface of the base material using high-purity gas having a purity of99.5% by volume or more shown in Table 1 or 2 under the depositionconditions shown in Table 1 or 2 so that the coating film was comprisedof the film structures each having the average thickness shown in Table3. Table 1 shows the deposition conditions for inner films and Table 2shows the deposition conditions for outer films including anintermediate film, and, in invention samples 1 to 6, chain hydrocarbonhaving carbon atoms of 2 or 3 was used as raw material gas.

TABLE 1 Sample Composition of raw Temperature Pressure Flow rate No.Type of film material gas (mol %) (° C.) (kPa) (L/min) InventionInnermost TiN TiCl₄: 2.4%, N₂: 48.8%, H₂: 48.8% 880 40.0 30.7 samplesfilm 1, 2 TiCN columnar TiCl₄: 1.5%, CH₃CN: 0.3%, C₂H₆: 880 8.0 15.8crystal film 3.2%, H₂: 95.0% Invention Innermost TiN TiCl₄: 2.4%, N₂:48.8%, H₂: 48.8% 830 40.0 30.7 samples film 3, 4 TiCN columnar TiCl₄:3.0%, CH₃CN: 0.2%, C₂H₄: 830 8.0 15.7 crystal film 2.1%, H₂: 94.7%Invention Innermost TiN TiCl₄: 2.4%, N₂: 48.8%, H₂: 48.8% 780 40.0 30.7samples film 5 TiCN columnar TiCl₄: 3.0%, CH₃CN: 0.2%, C₃H₆: 780 8.015.7 crystal film 1.2%, H₂: 95.6% Invention Innermost TiN TiCl₄: 2.4%,N₂: 48.8%, H₂: 48.8% 780 40.0 30.7 samples film 6 TiCN columnar TiCl₄:2.9%, CH₃CN: 0.1%, C₃H₆: 780 8.0 15.7 crystal film 1.6%, H₂: 95.4%Compara- Innermost TiN TiCl₄: 2.4%, N₂: 48.8%, H₂: 48.8% 880 40.0 30.7tive film samples TiCN columnar TiCl₄: 1.1%, CH₃CN: 1.3, N₂: 48.8%, 8808.0 20.5 1, 2 crystal film H₂: 48.8% Compara- Innermost TiN TiCl₄: 2.4%,N₂: 48.8%, H₂: 48.8% 880 40.0 30.7 tive film samples TiCN columnarTiCl₄: 3.0%, CH₃CN: 0.8%, H₂: 96.2% 880 8.0 15.6 3 crystal film Compara-Innermost TiN TiCl₄: 2.4%, N₂: 48.8%, H₂: 48.8% 830 40.0 30.7 tive filmsamples TiCN columnar TiCl₄: 3.0%, CH₃CN: 0.3%, H₂: 96.7% 830 8.0 15.64, 5 crystal film Compara- Innermost TiN TiCl₄: 2.4%, N₂: 48.8%, H₂:48.8% 950 40.0 30.7 tive film samples TiCN columnar TiCl₄: 1.2%, CH₃CN:0.2%, CH₄: 950 24.0 18.8 6 crystal film 16.0%, HCl: 2.7%, H₂: 79.9%

TABLE 2 Sample Composition of raw Temperature Pressure Flow rate No.Type of film material gas (mol %) (° C.) (kPa) (L/min) InventionIntermediate film TiCl₄: 2.2%, CO: 3.9%, H₂: 93.9% 980 18.7 12.8 samples(TiCO) 1 and Aluminum oxide AlCl₃: 2.5%, CO₂: 4.5%, CO: 4.4%, 980 7.316.1 Compara- film HCl: 4.0%, H₂S: 0.4%, H₂: 84.2% tive (κ-Al₂O₃)samples Outermost TiN TiCl₄: 0.8%, N₂: 49.6%, H₂: 49.6% 980 40.0 30.2 1film Invention Intermediate film TiCl₄: 0.9%, AlCl₃: 0.8%, N₂: 44.8%,1000 8.0 33.5 samples (TiAlCNO) CO: 0.9%, H₂: 52.6% 2~6 and Aluminumoxide AlCl₃: 0.9%, CO₂: 2.6%, CO: 10.4%, 1000 8.0 23.1 Compara- filmHCl: 6.5%, H₂S: 0.4%, H₂: 79.2% tive (α-Al₂O₃) samples Outermost TiNTiCl₄: 0.8%, N₂: 49.6%, H₂: 49.6% 1000 40.0 30.2 2~6 film

TABLE 3 Film structures and average thickness of each film(μm) AverageInner film Intermediate film thickness Sample Innermost TiCN columnarIntermediate Aluminum Outermost of coating No. TiN film crystal filmfilm oxide film TiN film film (μm) Invention 1.0 8.0 0.2(TiCO)4.9(κ-Al₂O₃) 0.5 14.6 samples 1 Invention 1.0 7.9 0.5(TiAlCNO)4.7(α-Al₂O₃) 0.3 14.4 samples 2 Invention 0.3 13.2 0.7(TiAlCNO)9.4(α-Al₂O₃) 0.3 23.9 samples 3 Invention 0.3 18.8 0.6(TiAlCNO)1.6(α-Al₂O₃) 0.3 21.6 samples 4 Invention 0.2 8.3 0.8(TiAlCNO)3.1(α-Al₂O₃) 0.4 12.8 samples 5 Invention 0.2 5.8 0.7(TiAlCNO)1.8(α-Al₂O₃) 0.2 8.7 samples 6 Comparative 1.0 7.9 0.2(TiCO)4.8(κ-Al₂O₃) 0.5 14.4 samples 1 Comparative 1.1 8.0 0.6(TiAlCNO)5.0(α-Al₂O₃) 0.4 15.1 samples 2 Comparative 1.1 19.3 0.5(TiAlCNO)3.9(α-Al₂O₃) 0.2 25.0 samples 3 Comparative 0.3 10.1 0.8(TiAlCNO)9.1(α-Al₂O₃) 0.3 20.6 samples 4 Comparative 0.3 6.1 0.8(TiAlCNO)3.1(α-Al₂O₃) 0.3 10.6 samples 5 Comparative 1.3 10.2 0.6(TiAlCNO)4.1(α-Al₂O₃) 0.3 16.5 samples 6

For the obtained invention samples 1 to 6 and comparative samples 1 to6, an X-ray diffraction analysis was conducted using CuKα radiation tomeasure a diffraction angle 2θ of the peak ascribed to the (422) crystalfacet of the TiCN columnar crystal film, a value of the half width ofthe peak, and a crystal face of the peak at which the TiCN columnarcrystal film has the highest intensity in the X-ray diffraction pattern.Next, a cross-section of the coating film cut in the directionperpendicular to the surface of the base material was subjected tomirror polishing, and a C content and a N content of the TiCN columnarcrystal film were quantitatively determined by EPMA, and a C/(C+N) ratioof the TiCN film was calculated. Further, the resultant sample wassubjected to heat treatment in a vacuum at 1,200° C. for 10 minutes todiffuse the metallic bonding phase of the cemented carbide base materialthrough the grain boundary in the TiCN columnar crystal coating film,and then the mirror polished surface of the normal cross-section wasexamined under a SEM to take a photomicrograph. On the photomicrographof the TiCN columnar crystal film at its middle portion, a line parallelto the interface of the cemented carbide base material was drawn, andthe number of grain boundaries in the TiCN columnar crystal film on theline having an arbitrary length was measured, and an average grain sizeof the film was calculated. The results are shown in Table 4.

TABLE 4 TiCN columnar crystal film Diffraction Value of half Crystalface of peak at Average angle 2θ of width of peak which TiCN columnargrain size peak ascribed ascribed crystal film has highest in directionto (422) to (422) intensity in X-ray C/(C + N) parallel to base SampleNo. crystal facet crystal facet diffraction pattern Ratio material (μm)Invention 122.4° 0.42° (111) 0.74 0.42 samples 1 Invention 122.4° 0.41°(111) 0.75 0.46 samples 2 Invention 122.1° 0.46° (422) 0.81 0.20 samples3 Invention 122.1° 0.44° (422) 0.81 0.21 samples 4 Invention 122.1°0.49° (422) 0.82 0.14 samples 5 Invention 121.8° 0.56° (422) 0.90 0.08samples 6 Comparative 123.5° 0.29° (111) 0.50 0.45 samples 1 Comparative123.5° 0.29° (111) 0.51 0.44 samples 2 Comparative 123.1° 0.33° (111)0.60 0.37 samples 3 Comparative 123.1° 0.38° (422) 0.59 0.25 samples 4Comparative 123.1° 0.38° (422) 0.60 0.26 samples 5 Comparative 122.3°0.28° (220) 0.78 1.13 samples 6

With respect to each of the cutting chips of invention samples 1 to 6and comparative samples 1 to 6, a cutting test was conducted under theconditions shown below using, as a material to be cut, doughnut discFCD700 (hardness: HB240) having an outer diameter of 180 mm, an innerdiameter of 60 mm, and a thickness of 20 mm.

Cutting Test

Cutting speed: Vc=250 m/min

Cut depth: ap=2 mm

Feed: f=0.35 mm/rev

Coolant: Water-soluble cutting liquid used

Cutting mode: One pass cutting for each of the both edge faces per onedoughnut disc material is continuously performed.

Cutting performance: The number of the doughnut disc materials cut untilthe cut material has a thickness larger by 0.05 mm than the averagethickness of the 4 th to 6 th materials from the start of the cutting isused as cutting performance of the cutting chip.

With respect to each of invention samples 1 to 6 and comparative samples1 to 6, the number of the cut materials and the damage of the cuttingchip after the cutting test are shown in Table 5.

TABLE 5 Number of Sample No. cut materials Damage Invention 102 Normalwear samples 1 Invention 115 Normal wear samples 2 Invention 170 Normalwear samples 3 Invention 180 Normal wear samples 4 Invention 143 Normalwear samples 5 Invention 145 Normal wear samples 6 Comparative 35Chipping samples 1 Comparative 45 Chipping samples 2 Comparative 36Fracture samples 3 Comparative 61 Normal wear samples 4 Comparative 44Normal wear samples 5 Comparative 17 Fracture samples 6

As can be seen from Table 5, invention samples 1 to 6 individually haveexcellent wear resistance, excellent resistance to chipping, andexcellent fracture resistance, and hence are unlikely to cause backwardmovement of the tool edge position, and exhibit the large number of thematerials to be cut, as compared to comparative samples 1 to 6.

1.-15. (canceled)
 16. A method for producing a coated cutting toolcomprising depositing a TiCN columnar crystal film by a CVD method at atemperature in the range of from 700 to 900° C. using raw material gascomprising a chain hydrocarbon having carbon atoms of from 2 to 20, anorganic cyanogen compound, titanium tetrachloride, and hydrogen.
 17. Thecoated cutting tool according to claim 16, wherein a value of the halfwidth of the peak ascribed to the (422) crystal facet of the TiCNcolumnar crystal film is 0.40 to 0.60°.
 18. The coated cutting toolaccording to claim 16, wherein the TiCN columnar crystal film exhibitsan X-ray diffraction pattern having the highest intensity at the peakascribed to the (422) crystal facet.
 19. The coated cutting toolaccording to claim 16, wherein the atomic ratio of carbon to the sum ofcarbon and nitrogen contained in the TiCN columnar crystal film{C/(C+N)} is 0.70 to 0.90.